Optical switching element, and switching device and image display apparatus each using the optical switching element

ABSTRACT

An optical switching element having a simple configuration and high response and capable of performing gradation display by area gradation is provided. In a state where a light extracting portion is in contact with an upper substrate, light enters the light extracting portion from the upper substrate, emits from the back face of the light extracting portion, is passed through a lower substrate, and becomes transmission light. In a state where the light extracting portion is attracted by the lower substrate side, the incident light is totally reflected by a total reflection face, and total reflection light emits from a V-shaped groove. The incident light can be switched in two directions and obtained as the transmission light and the total reflection light. To display one pixel, in the light extracting portion and a plurality of other light extracting portions, the incident light is selectively taken by being switched between two directions of the transmission light and the total reflection light, thereby enabling the gradation display by area gradation to be performed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical switching element capable ofpolarizing incident light into two directions, and an optical switchingdevice and an image display apparatus each using the optical switchingelement.

2. Description of the Related Art

In recent years, importance of a display as a display device of imageinformation is increasing. As an element for the display and, further,as elements for optical communication, an optical memory device, anoptical printer, and the like, development of an optical switchingelement operating at high speed is in demand. Conventionally, elementsof this kind include an element using a liquid crystal, an element usinga micromirror, an element using a diffraction grating, and the like.FIG. 1 shows an example of the element using a liquid crystal. FIGS. 2Aand 2B to FIG. 5 show examples of the elements using micromirrors. FIGS.6A and 6B show an example of the element using a diffraction grating.

An optical switching element using a liquid crystal (FIG. 1) includestwo polarizing plates 101 a and 101 b, two glass substrates 102 a and102 b, transparent electrodes 103 a, 103 b, 103 c, and 103 d, and aliquid crystal 104 sealed between the glass substrates 102 a and 102 b.The optical switching element performs switching operation by applying avoltage across the transparent electrodes 103 a, 103 b, 103 c, and 103 dto control the directions of liquid crystal molecules, thereby rotatinga plane of polarization.

The liquid crystal has, however, response of only about a fewmilliseconds at the highest and therefore has a problem such that theliquid crystal has a characteristic of low response. Consequently, it isvery difficult to apply the liquid crystal to optical communication,optical calculation, optical memory device such as a hologram memory,optical printer, and the like requiring fast response. Since the opticalswitching element using the liquid crystal needs two polarizing plates,there is also a problem that efficiency of light utilization decreases.Further, since the liquid crystal is not resistive to strong light,light having high energy density such as a strong laser beam cannot beswitched. Particularly, in the case of using the optical switchingelement for a display, higher image quality as compared with that ofoptical switching elements of recent years is requested. The opticalswitching element using the liquid crystal of current conditions startsto be insufficient with respect to accuracy in gradation display.

As for the optical switching element using a micromirror, there arealready a number of examples typified by the DMD (Digital MicromirrorDevice) of Texas Instruments Incorporated (U.S.). The examples of theDMD can be broadly divided into two kinds with respect to the structure;a structure in which a micromirror is supported by one side (FIGS. 2Aand 2B and FIG. 3) and a structure in which a micromirror is supportedby both sides (FIGS. 4A and 4B and FIG. 5). Micromirror driving methodsinclude a method using electrostatic attraction, a method using apiezoelectric device, and a method using a thermal actuator. In spite ofdifference in structure, driving method, and the like, the function ofswitching incident light by controlling the angle of a micromirror is avery simple one.

A micromirror of a type using electrostatic attraction will be describedhere as an example. The driving principle of the micromirror is asfollows. In the case where a micromirror 105 is supported by one side(FIGS. 2A and 2B and FIG. 3), by giving a potential difference betweenthe micromirror 105 and a drive electrode 106, the electrostaticattraction is generated to make the micromirror 105 tilt. When the givenpotential difference is eliminated, the micromirror 105 returns to itsoriginal state by spring force of a hinge 105 a supporting themicromirror 105.

In the case where the micromirror is supported by both sides (FIGS. 4Aand 4B and FIG. 5), the same potential difference is created between amicromirror 108 and two electrodes 107 a and 107 b facing themicromirror 108. From such a state, for example, by decreasing a voltageapplied to one, 107 a, of the electrodes and increasing a voltageapplied to the other electrode 107 b, unbalance is caused between theelectrostatic attraction generated between the electrode 107 a and themicromirror 108 and the electrostatic attraction generated between theelectrode 107 b and the micromirror 108, thereby making the micromirror108 tilt.

Light is switched as follows. In the case of the micromirror supportedby one side (FIGS. 2A and 2B and 3), in a state where the micromirror105 is not tilted with respect to incident light P₁₀₀, reflection lighttravels in a direction P₁₀₁. In a state where the micromirror 105 tiltswith respect to the incident light P₁₀₀, reflection light travels in adirection P₁₀₂. In the case of the micromirror supported by both sides(FIGS. 4A and 4B and FIG. 5), similarly, in a state where themicromirror 108 tilts in one direction with respect to incident lightP₁₀₀, reflection light travels in a direction P₁₀₃. In a state where themicromirror 108 tilts in another direction with respect to the incidentlight P₁₀₀, reflection light travels in a direction P₁₀₄.

The response is, however, about a few microseconds in many cases. Itcannot be said the speed is high enough. In order to perform gradationdisplay by a digital control using time division, one micromirror isnecessary per pixel in an image, that is, a two-dimensional micromirrorarray is necessary. It is considered that the demand on the higher imagequality is increasing more and more. In this case, manufacturing of anecessary two-dimensional micromirror array will become very difficult.In an optical switching element using the micromirrors, a lightpolarizable angle (angle difference between two reflection light) isabout twice as large as a mechanical mirror runout angle. However, inthe case of using the optical switching element for a display, to makethe contrast high, the angle difference between the two reflection lightP₁₀₃ and P₁₀₄ has to be set large. It causes a problem that the responsedeteriorates more.

In the optical switching device using a diffraction grating (FIGS. 6Aand 6B), as disclosed in Translated National Publication of PatentApplication No. Hei10-510374, a ribbon-shaped movable mirror 109 a ismoved by a quarter of the wavelength of the incident light P₁₀₀ byelectrostatic attraction generated by making a potential differencebetween the movable mirror 109 a and a lower electrode 110 a, so that anoptical path difference corresponding to the half of the wavelength iscaused between a ribbon-shaped stationary mirror 109 b and the movablemirror 109 a, thereby generating diffraction light. The reflection lightis switched between the direction of zero-order diffraction light P₁₀₅and the direction of primary diffraction light P₁₀₆. In this case, bycontrolling the optical path difference within the range to the halfwave, the intensity of the primary diffraction light P₁₀₆ can becontrolled. In an optical switching device using a diffraction grating,only by moving a very light ribbon-shaped mirror by a short distance,light can be switched. Consequently, the optical switching device hasfast response (about tens nanoseconds) and is suitable for high-speedswitching.

The primary diffraction light is, however, generated with certain anglesin two directions symmetrical to the optical axis of the zero-orderdiffraction light. Consequently, in order to use the primary diffractionlight, a complicated optical system for collecting light traveling inthe two directions to a single light is necessary. To make the lightdiffract, at least two ribbon-shaped mirrors are necessary per pixel. Inorder to increase the efficiency of light utilization, four or more,actually, six ribbon-shaped mirrors are necessary. In a light valve(spatial light modulator) in which a necessary number of pixels of theribbon-shaped mirrors six per pixel are formed in an array, it isdesired that a reflection face of the stationary mirror 109 b and areflection face of the movable mirror 109 a are flush with each other toavoid generation of the primary diffraction light without applyingvoltage to the electrodes. In practice, however, the reflection facesare not easily adjusted to be flush with each other. Fine adjustment istherefore necessary to make all of the reflection faces flush with eachother by applying a low voltage to each of lower electrodes 110 a and110 b.

SUMMARY OF THE INVENTION

The invention has been achieved in view of the problems. A first objectof the invention is to provide a small, light optical switching elementhaving a simple structure and high response, and capable of performinggradation display by area gradation in an image display apparatus and anoptical switching device using the optical switching element.

A second object of the invention is to provide an image display capableof performing gradation display of ultra-high precision by using theoptical switching element and obtaining high image quality.

An optical switching element according to the invention comprises: atotal reflection member having a total reflection face by which incidentlight can be totally reflected; and a plurality of translucent lightextracting portions constructing one pixel, each of which can beswitched between a first position at which the light extracting portioncomes into contact with or is close to the total reflection face of thetotal reflection member in a distance in which near field light can beextracted and a second position apart from the total reflection face bymore than the distance in which the near field light can be extracted.

An optical switching device according to the invention has a pluralityof optical switching elements according to the invention which arearranged one-dimensionally or two-dimensionally.

An image display according to the invention having a plurality ofoptical switching elements according to the invention arranged displaysa two-dimensional image by irradiating the plurality of opticalswitching elements with light of three primary colors and scanning lightby a scanner.

In the optical switching element, optical switching device, and imagedisplay according to the invention, when the light extracting portion isin the second position, the total reflection member and the translucentlight extracting portion are apart from each other. Consequently,incident light on the total reflection member is totally reflected bythe total reflection face, and its reflection light is led in onedirection. When the light extracting portion is in the first position,the total reflection member and the light extracting portion are incontact with each other or are close to each other. Consequently,incident light on the total reflection member is not totally reflectedbut is led to another direction opposite to the total reflection membervia the light extracting portion. Thus, by selectively switching each ofthe light extracting portions between the first and second positionswith respect to one pixel, gradation display by area gradation can beperformed. The expression “to be close to the total reflection face in adistance in which near field light can be extracted” denotes that thelight extracting portion does not have to be in perfect contact with thetotal reflection member but is sufficient that the light extractingportion is in a distance so that incident light can be extracted. Whenthe light extracting portion is close to the total reflection member ina distance of about {fraction (1/40)} of the wavelength (λ) of incidentlight, 90% or more of incident light can be extracted.

Other and further objects, features and advantages of the invention willappear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a structure of a conventional optical switchingelement using liquid crystal.

FIGS. 2A and 2B are views showing structure of a conventional opticalswitching element using a micromirror (of one-side support type).

FIG. 3 is a view for explaining an action of the optical switchingelement of FIGS. 2A and 2B.

FIGS. 4A and 4B are views showing a structure of a conventional opticalswitching element using a micromirror (of both-side support type).

FIG. 5 is a view for explaining an action of the optical switchingelement of FIGS. 4A and 4B.

FIGS. 6A and 6B are views for explaining an action of a conventionaloptical switching element using a diffraction grating.

FIG. 7 is a perspective view showing the configuration of an opticalswitching device according to an embodiment of the invention.

FIGS. 8A and 8B are plan view and cross section for explaining amanufacturing process of the optical switching device shown in FIG. 7.

FIG. 9 is a plan view for explaining a process following the process ofFIGS. 8A and 8B.

FIG. 10 is a cross section for explaining a process following theprocess of FIG. 9.

FIGS. 11A and 11B are plan view and cross section for explaining aprocess following the process of FIG. 10.

FIG. 12 is a cross section for explaining a process following theprocess of FIGS. 11A and 11B.

FIG. 13 is a cross section for explaining a process following theprocess of FIG. 12.

FIG. 14 is a cross section for explaining a process following theprocess of FIG. 13.

FIG. 15 is a cross section for explaining a process following theprocess of FIG. 14.

FIGS. 16A and 16B are plan views for explaining a process following theprocess of FIG. 15.

FIG. 17 is a cross section for explaining a process following theprocess of FIGS. 16A and 16B.

FIGS. 18A and 18B are cross sections for explaining a process followingthe process of FIG. 17.

FIGS. 19A and 19B are plan views for explaining a process following theprocess of FIGS. 18A and 18B.

FIG. 20 is a cross section for explaining a process following theprocess of FIGS. 19A and 19B.

FIGS. 21A and 21B are cross sections for explaining the operation of theoptical switching device shown in FIG. 7.

FIG. 22 is an explanatory diagram showing an example of a method ofgradation display combining area gradation display and gradation displayby time division per pixel in the optical switching device shown in FIG.7.

FIGS. 23A and 23B are cross sections for explaining a modification ofthe optical switching device shown in FIG. 7.

FIGS. 24A and 24B are cross sections for explaining another modificationof the optical switching device shown in FIG. 7.

FIGS. 25A and 25B are cross sections for explaining further anothermodification of the optical switching device shown in FIG. 7.

FIGS. 26A and 26B are cross sections for explaining further anothermodification of the optical switching device shown in FIG. 7.

FIGS. 27A and 27B are cross sections for explaining further anothermodification of the optical switching device shown in FIG. 7.

FIGS. 28A and 28B are cross sections for explaining further anothermodification of the optical switching device shown in FIG. 7.

FIGS. 29A and 29B are cross sections for explaining further anothermodification of the optical switching device shown in FIG. 7.

FIG. 30 is a configuration diagram of a display to which the opticalswitching device shown in FIG. 7 is applied.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the invention will be described in detail hereinbelowwith reference to the drawings.

FIG. 7 shows a partial configuration of an optical switching device 1according to an embodiment of the invention. In FIG. 7, although theoptical switching device 1 having an optical switching element 10 acorresponding to one pixel is expressed for simplicity, the opticalswitching device 1 of the invention has a one-dimensional arraystructure having a plurality of optical switching elements 10. By theoptical switching device 1, for example, an image display which will bedescribed herein later is constructed.

The optical switching device 1 has a translucent upper substrate 11 anda translucent lower substrate 21 disposed so as to face the uppersubstrate 11. Each of the upper substrate 11 and the lower substrate 21is a translucent substrate which is, for example, a glass substrate or atransparent plastic substrate.

The top face and the under face of the upper substrate 11 are parallelto each other. In the top face, a V-shaped groove 11 a as a lightincident portion and a V-shaped groove 11 b as a light emitting portionare formed. On the top face including the V-shaped grooves 11 a and 11b, an anti reflection film 12 made of, for example, MgF₂ (magnesiumfluoride) is formed. The under face of the upper substrate 11 is a totalreflection face 11A for totally reflecting incident light. The angle ofinclination of each of the V-shaped grooves 11 a and 11 b is an angleequal to or larger than a critical angle for totally reflecting lightentering from a direction perpendicular to the inclined face by thetotal reflection face 11A.

On the total reflection face 11A side of the upper substrate 11,although not shown, an upper transparent electrode made of, for example,ITO (Indium-Tin Oxide; a mixed film of indium-tin oxide) is formed. Onthe total reflection face 11A side of the upper substrate 11, forexample, four thin ribbon-shaped light extracting portions 17 a, 17 b,17 c, and 17 d made of silicon nitride (SiNx) are disposed. The ratio ofwidths (areas) of the light extracting portions 17 a, 17 b, 17 c, and 17d is desirably 2^(n) (where n is an integer of 0 or larger) and is, forexample, 1:2:4:8. In the embodiment, one pixel in an image display isconstructed by the four light extracting portions 17 a to 17 d. Thelight extracting portions 17 a to 17 d are shown by being separated fromthe upper substrate 11 to make the structure understood easier in FIG.7.

Each of the light extracting portions 17 a, 17 b, 17 c, and 17 d has abridge structure including both ends supported by the upper substrate 11and an intermediate portion which is switchable between a first positionand a second position. In the first position, by electrostaticattraction generated by a potential difference due to application of avoltage to the transparent electrode, the intermediate portion is incontact with the total reflection face 11A of the upper substrate 11 oris close to the total reflection face 11A within a distance in whichnear field light can be extracted (state of the light extractingportions 17 a and 17 d in FIG. 7). In the second position, theintermediate portion is apart from the total reflection face 11A morethan the distance in which the near field light can be extracted (stateof the light extracting portions 17 b and 17 c in FIG. 7). Driving meansof the invention is constructed by the transparent electrode and voltageapplying means (not shown) formed on the total reflection face 11A ofthe upper substrate 11, light extracting portions 17 a, 17 b, 17 c, and17 d, and the top face of the lower substrate 21.

On the lower substrate 21, a plurality of spacers 24 a and a pluralityof inter-substrate spacers 25 are formed. Each of the spacers 24 a andthe inter-substrate spacers 25 is formed by, for example, apolycrystalline silicon film. The spacer 24 a functions as a stopper andsupporting portion when the light extracting portions 17 a, 17 b, 17 c,and 17 d are displaced to the second position. In this case, the spacers24 a are provided in two lines along the arranging direction of thelight extracting portions 17 a, 17 b, 17 c, and 17 d. Theinter-substrate spacer 25 is used to maintain an interval between thelower substrate 21 and the upper substrate 11 so that the lightextracting portions 17 a, 17 b, 17 c, and 17 d can be displaced betweenthe first and second positions. Although not shown, on the face on whichthe spacers 24 a and the inter-substrate spacers 25 are formed of thelower substrate 21, an upper transparent electrode made of, for example,ITO is formed.

In the embodiment, the optical switching element 10 of one linecorresponding to one pixel is constructed by the four light extractingportions 17 a, 17 b, 17 c, and 17 d having different widths (areas). Aplurality of optical switching elements 10 are arranged in an array,thereby constructing the one-dimensional optical switching device 1.

A specific manufacturing method of the optical switching device 1 willnow be described. The manufacturing process of the optical switchingdevice 1 having the optical switching element 10 constructed by the fourlight extracting portions 17 a, 17 b, 17 c, and 17 d having differentwidths (areas) will now be described.

First, as shown in FIGS. 8A and 8B, on the top face of the uppersubstrate 11 which is a translucent substrate, for example, a glasssubstrate, the V-shaped groove 11 a serving as a light incident portionand the V-shaped groove 11 b serving as a light emitting portion areformed by, for example, physical process such as etching or mechanicalprocess such as process using a grinder. Subsequently, AR(anti-reflection) coating is performed on the face in which the V-shapedgrooves 11 a and 11 b are formed by, for example, vacuum evaporation tothereby form the anti reflection film 12 made of, for example, MgF₂. Onthe face (total reflection face 11A) opposite to the face in which theV-shaped grooves 11 a and 11 b are formed, for example, by CVD (ChemicalVapor Deposition), the transparent electrode (such as ITO film) having athickness of, for instance, 50 nm and a (transparent) insulating film(such as silicon oxide (SiO₂) film) having a thickness of, for example,30 nm are formed in this order. A stacked film 13 including the uppertransparent electrode is patterned in an electrode shape (shapecorresponding to the light extracting portions 17 a, 17 b, 17 c, and 17d) by etching. The insulating film serves as a protective film of theupper transparent electrode (ITO film).

As shown in FIG. 9, a light absorption layer 14 for absorbingunnecessary light is formed so as to be thinner than the electrodebetween the electrode patterns by, for example, vacuum evaporation.Subsequently, as shown in FIG. 10, a sticking preventing layer 15 havinga thickness of, for example, 2 nm made of a fluoroplastic or the like isformed. On the sticking preventing layer 15, a sacrifice layer 16 havinga thickness of, for example, 400 nm made of amorphous silicon (a-Si) orthe like is formed and patterned in the shapes of the light extractingportions 17 a, 17 b, 17 c, and 17 d by etching. The sticking preventinglayer 15 is used to prevent the thin ribbon-shaped light extractingportion 17 a described hereinlater from being stuck to the uppersubstrate 11. The sacrifice layer 16 is provided to manufacture thelight extracting portions 17 a, 17 b, 17 c, and 17 d so as to have thebridge structure in which the intermediate portion of each of the lightextracting portions 17 a, 17 b, 17 c, and 17 d is apart from the totalreflection face 11A of the upper substrate 11 by a half wave or more.

Subsequently, as shown in FIGS. 11A and 11B, as the structural materialof the light extracting portions 17 a, 17 b, 17 c, and 17 d, a siliconnitride film 17 having a thickness of, for example, 100 nm is formed by,for example, LPCVD (Low Pressure Chemical Vapor Deposition). As shown inFIG. 12, an ITO film 18 is formed as a transparent movable electrodehaving a thickness of, for example, 50 nm and an aluminum (Al) film 19having a thickness of, for example, 20 nm is formed on the ITO film 18.The aluminum film 19 functions as a protective layer of the ITO film 18when a silicon oxide film (SiO₂) 20 which will be described hereinlateris tapered.

After that, a tapering process is performed so that light entering thelight extracting portions 17 a, 17 b, 17 c, and 17 d is not totallyreflected by the back face of the light extracting portions 17 a, 17 b,17 c, and 17 d. In order to perform the process, first, as shown in FIG.13, the silicon oxide film 20 having a thickness of, for example, 1 μmis formed by LPCVD or the like. Subsequently, as shown in FIG. 14, aresist film 21 is applied on the silicon oxide film 20 and is exposed byusing a gray scale mask to be processed in a tapered shape.Subsequently, as shown in FIG. 15, by selectively removing the siliconoxide film 20 by using the tapered resist film 21 as a mask by, forexample, RIE (Reactive Ion Etching), a tapered portion 20 a is formed.

As shown in FIGS. 16A and 16B, the silicon nitride film 17, ITO film 18,aluminum film 19, tapered portion 20 a, sticking preventing layer 15,and sacrifice layer 16 are patterned in shapes corresponding to thelight extracting portions 17 a, 17 b, 17 c, and 17 d by dry etching.After that, the sacrifice layer 16 made of amorphous silicon is removedby dry etching using xenon fluoride (XeF₂). By the operation, thesilicon nitride film 17 is formed into the thin ribbon-shaped lightextracting portions 17 a, 17 b, 17 c, and 17 c having the bridgestructure. The widths (areas) of the four light extracting portions 17a, 17 b, 17 c, and 17 d are set at a ratio of, for example, 1:2:4:8.

As shown in FIG. 17, the lower substrate 21 disposed on the sideopposite to the light incident side is prepared. One of the faces of thelower substrate 21 is subjected to, for example, AR (anti-reflection)coating to form an anti-reflection film 22 made of MgF₂ for preventinginner face reflection. On the face of the lower substrate 21 opposite tothe anti-reflection film 22 side, for example, an ITO film serving as alower transparent electrode, an insulating layer such as a silicon oxide(SiO₂) film, and an anti-reflection film made of MgF₂ are sequentiallyformed in accordance with this order to form a stack film 23. Further,on the stack film 23, a polycrystalline silicon film 24 having athickness of, for example, 1.1 μm is formed by LPCVD or the like.

As shown in FIGS. 18A and 18B, the polycrystalline silicon film 24 ispatterned to form the spacers 24 a for preventing contact between thelight extracting portions 17 a, 17 b, 17 c, and 17 d formed on the uppersubstrate 11 side in the preceding process and the lower transparentelectrode (ITO film) on the lower substrate 21 side. Subsequently, thestack film 23 is patterned in an electrode shape (shape corresponding tothe light extracting portions 17 a, 17 b, 17 c, and 17 d formed on theupper substrate 11 side).

As shown in FIGS. 19A and 19B, a polycrystalline silicon film having athickness of, for example, 2.2 μm is formed. By patterning thepolycrystalline silicon film, the inter-substrate spacers 25 between theupper substrate 11 on which the light extracting portions 17 a, 17 b, 17c, and 17 d are formed and the lower substrate 21 on which the lowertransparent electrode is formed are formed.

Finally, as shown in FIG. 20, the upper substrate 11 and the lowersubstrate 21 are joined to each other with the inter-substrate spacers25 inbetween by using In (indium) as a joint layer, thereby finishing aseries of processes. The optical switching device 1 including theoptical switching elements 10 each having the four light extractingportions 17 a, 17 b, 17 c, and 17 d having different widths (areas) iscompleted.

The aspect ratio in the drawings used for explaining the manufacturingprocess is different from an actual one for easier understanding. Inpractice, for example, the length of the movable portion of each of theribbon-shaped light extracting portions 17 a, 17 b, 17 c, and 17 d is120 μm, the widths of the light extracting portions 17 a, 17 b, 17 c,and 17 d are 4 μm, 8 μm, 16 μm, and 32 μm, respectively, and thedistance between the neighboring light extracting portions 17 a is 0.5μm.

The operation of the thin ribbon-shaped light extracting portion 17 a asa component of the optical switching element 10 according to theembodiment will be described with reference to FIGS. 21A and 21B. Theoperations of the other three light extracting portions 17 b, 17 c, and17 d are similar to the operation of the light extracting portion 17 a,and the light extracting portions 17 a, 17 b, 17 c, and 17 d can bedriven independent of each other.

A transparent movable electrode (not shown) formed on the thinribbon-shaped light extracting portion 17 a is grounded to set thepotential as 0V, and a voltage of, for example, +12V is applied to theupper transparent electrode (not shown) formed on the upper substrate11. By the potential difference, electrostatic attraction is generatedbetween the light extracting portion 17 a and the upper substrate 11. Asshown in FIG. 21A, the light extracting portion 17 a comes into contactwith the upper substrate 11 (first position). In this state, light P₁ isperpendicularly incident on an inclined face of the V-shaped groove 11 ain the upper substrate 11. The incident light P₁ passes through theupper substrate 11, enters the light extracting portion 17 a, emits fromthe tapered portion 20 a formed on the back face of the light extractingportion 17 a, after that, transmits the lower substrate 21, and convertsas transmission light P2.

After that, the light extracting portion 17 a is separated from theupper substrate 11 into a state of FIG. 21B. Specifically, the uppertransparent electrode (not shown) formed on the upper substrate 11 isgrounded to set the potential as 0V and, simultaneously, a voltage of,for example, +12V is applied to the lower transparent electrode (notshown) formed on the lower substrate 21. By the potential difference,electrostatic attraction is generated between the lower transparentelectrode and the transparent movable electrode on the light extractingportion 17 a having the potential of 0V, and the light extractingportion 17 a is attracted by the lower substrate 21 side. At this time,the light extracting portion 17 a comes into contact with the spacer 24a on the lower substrate 21 and is stopped (second position). In thisstate, the incident light P₁ is totally reflected by the under face(total reflection face 11A) of the upper substrate 11, and emits astotal reflection light P₃ from the other V-shaped groove 11 b processedseparately from the V-shaped groove on the incident side.

As described above, according to the embodiment, by the operation of thelight extracting portion 17 a, the incident light P₁ can be switched inthe two directions and taken as the transmission light P₂ and the totalreflection light P₃. In the optical switching element 10, the movableportion is only the light extracting portion 17 a, and the distance ofmovement of the light extracting portion 17 a is at most about onewavelength of incident light. Consequently, the switching operation isperformed at very high speed. Since electrodes can be formed on andunder the light extracting portion 17 a as the movable portion, fastresponse can be achieved irrespective of a mechanical resonancefrequency.

In addition, in the optical switching element 10 of the embodiment, onepixel is constructed by the thin ribbon-shaped four light extractingportions 17 a, 17 b, 17 c, and 17 d having different widths (areas),which can be independently driven. In the case of performing gradationdisplay of an image, not only the gradation display by the time divisionbut also the area gradation display can be performed.

Specifically, an example of the gradation display method combining thearea gradation display and gradation display by time division per pixelwill be described by using FIG. 22. In this case, a gradation number canbe expressed by “area×time”. An image having a smaller gradation numberis dark, and an image having a large gradation number is light. That is,0 indicates the darkest state (black). In the embodiment, the ratio ofthe widths (areas) of the ribbon-shaped light extracting portions 17 a,17 b, 17 c, and 17 d is set as 1:2:4:8. Consequently, by combinations ofthe four values, the number of gradations which can be expressed by thearea gradation is 16 from 0 to 15. The number of gradations which can bedisplayed by time division is, when it is assumed that time is changedin, for example, 16 levels from 1 to 16. The number of the brightestgradation is 240 (=15×16). Since “0” is added to 240, gradation displayin 241 levels can be performed.

Only by the simply combination of time and area, gradation numbers areoverlapped. Consequently, only the portion of gradation numbersdisplayed in hollow numerals in FIG. 22 can be used for display, thenumber of gradations which can be displayed is 99, and gradation displayin 99 levels can be performed. When the gradation numbers areoverlapped, priority is given to one having longer time. The display ofthe remaining gradation numbers of 142 kinds (=241·99) is performed bycombining gradation numbers of 99 kinds displayed in hollow numerals.For example, in the case of displaying the gradation number 239, displayis performed in the area 15 for the time 15 and, after that, display isperformed in the area 14 for the remaining time 1. It is consequentlycalculated as 15×15+14×1=239. Display can be similarly performed withrespect to each of the other gradation numbers. In such a manner, thegradation display in 241 levels can be realized.

According to the embodiment as described above, by using the opticalswitching element 10 having the four thin ribbon-shaped light extractingportions 17 a, 17 b, 17 c, and 17 d of different widths (area), whichcan be independently driven, the combination of the area gradationdisplay and the gradation display by time division can be used in thesame pixel, and the gradation display of 241 levels can be carried out.By one-dimensionally arranging the optical switching elements 10,ultra-high definition can be achieved. Since the gradation display bydigital control can be performed, the optical switching element 10 withvery accurate gradation expression can be realized. For a resolution tothe extent used in a current TV system, it is possible to use one lightextracting portion per pixel and perform the gradation display only bytime division. If the resolution increases more and more in future, inthe case of performing the gradation display only by time division, notonly the optical switching element itself but also a drive circuit and asignal processing circuit are required to have very high frequencycharacteristics (hundreds MHz to a few GHz). In this case as well, inthe optical switching element 10 of the embodiment, the area gradationdisplay and the gradation display by time division can be combined.Consequently, the drive frequency can be set to be less than one tenths,and a load on the optical switching element 10, drive circuit, andsignal processing circuit can be lessened.

In the embodiment, both the total reflection light P₃ from the totalreflection face 11A of the upper substrate 11 and the transmission lightP₂ passed through the light extracting portions 17 a, 17 b, 17 c, and 17d can be used with respect to the incident light P₁, or either thetransmission light P₂ or the total reflection light P₃ can be used. Inthe case of using both the transmission light P₂ and the totalreflection light P₃, the element can be used as a two-way lightpolarization element having little crosstalk. In the case of using onlythe total reflection light P₃, a switching element of high lightefficiency can be constructed. In the case of using only thetransmission light P₂, an optical switching element having high contrastcan be constructed. The specific configuration in the case of using onlyone light will be described hereinlater.

In the optical switching element 10 using such a total reflectionmember, the incident light P₁ has to be incident on the total reflectionface 11A at an angle satisfying the total reflection condition. That is,in the case of using one side of the upper substrate 11 as a totalreflection face, when a glass substrate having both faces parallel toeach other is used as it is, light cannot be incident at an incidentangle (critical angle) satisfying the total reflection condition.

In contrast, in the embodiment, the V-shaped groove 11 a is formed inthe upper substrate 11 by etching, molding, mechanical process, or thelike, thereby enabling light to be incident at an incident angle equalto or larger the critical angle. Similarly, the V-shaped groove 11 b isformed in the emitting portion from the upper substrate 11 of the totalreflection light P₃ so that the total reflection light P₃ is not againtotally reflected by the surface of the upper substrate 11. In theembodiment, therefore, the total reflection light P₃ can be efficientlytaken from the incident light P₁.

In place of forming the V-shaped grooves 11 a and 11 b, by using amicroprism covering both the light incident portion and the reflectionlight emitting portion or microprisms each covering each of the incidentportion and the reflection light emitting portion, similar effects canbe expected. The V-shaped grooves 11 a and 11 b can be also replaced by,not only the microprism, but also a cylindrical lens covering both thelight incident portion and the reflection light emitting portion andhaving a center in the total reflection face. These specific exampleswill be described hereinlater as modifications.

In the embodiment, in the case of extracting light in a state where thelight extracting portion 17 a is made contact with the total reflectionface 11A of the upper substrate 11 or is set so close to the totalreflection face 11A that near-field light can be extracted, the processon extracted light in the light extracting portions 17 a, 17 b, 17 c,and 17 d becomes an issue. To be specific, when a face opposite to thelight extracting face of each of the light extracting portions 17 a, 17b, 17 c, and 17 d remains to be parallel and is not subjected to anyprocess, light does not emit from the opposite face but is totallyreflected. Consequently, the element does not function as the opticalswitching element. In the embodiment, therefore, by etching a faceopposite to the light extraction face of each of the light extractingportions 17 a, 17 b, 17 c, and 17 d, a portion (tapered portion 20 a)angled so that the incident angle of light becomes smaller than thecritical angle is provided, and light can emit from the tapered portion20 a.

By the operation, in the optical switching element 10, both thetransmission light P₂ of the light extracting portions 17 a, 17 b, 17 c,and 17 d and the total reflection light P₃ by the upper substrate 11 canbe used with respect to the incident light P₁. In the case of using theelement as the optical switching element using only the total reflectionlight P₃, by providing a light absorption layer on a face opposite tothe light extracting face of each of the light extracting portions 17 a,17 b, 17 c, and 17 d, light can be switched only in one direction (referto FIGS. 28A and 28B).

On the other hand, in the case of using the element as the opticalswitching element using only the transmission light P₂ of the lightextracting portions 17 a, 17 b, 17 c, and 17 d, the upper substrate 11remains to have a flat face without being subject to a process offorming the V-shaped groove in the emitting portion of the uppersubstrate 11 of the total reflection light P₃ or is processed so as tohave an angle of total reflection. In such a manner, total reflection iscarried out again, so that the reflection light does not emit from theupper substrate 11 but can be led through in the upper substrate 11 in adirection parallel to the upper substrate 11 (refer to FIGS. 27A and27B). In the case of such a configuration, however, light may beattenuated or seep through by an influence of a structure fabricated ona substrate or a layer formed, thereby causing deterioration incontrast. It is therefore necessary to pay attention fully. Similarly,in the case of an optical switching element using only the transmissionlight P₂ of the light extracting portions 17 a, 17 b, 17 c, and 17 d, byproviding the light absorption layer in place of forming the V-shapedgroove in the emitting portion in the upper substrate 11 of the totalreflection light P₃, light emitting from the upper substrate can beabsorbed (refer to FIGS. 26A and 26B).

In the embodiment, since the movable portions are only the ribbon-shapedlight extracting portions 17 a, 17 b, 17 c, and 17 d, the movableportions are small and light. To drive the movable portions, a strongforce is not necessary but the electrostatic attraction is sufficient.As the electrode for generating the electrostatic attraction, it is alsopossible to provide transparent electrodes for both the total reflectionface 11A of the upper substrate 11 and the light extracting portions 17a, 17 b, 17 c, and 17 d or to use an opaque conductive film, forexample, an aluminum (Al) film formed so as to avoid light transmittingportions.

In order to prevent the light extracting portions 17 a, 17 b, 17 c, and17 d from being stuck to the total reflection face 11A of the uppersubstrate 11, the transparent electrode is used also on the lowersubstrate 21 facing the upper substrate 11 so as to sandwich the lightextracting portions 17 a, 17 b, 17 c, and 17 d to make the totalreflection mirror face and the light extracting portions apart from eachother during a period in which switching is not performed and to driveat higher speed. Instead, an opaque electrode formed so as to avoidlight transmitting portions can be used.

For example, when the light extracting portions 17 a, 17 b, 17 c, and 17d can be sufficiently prevented from being stuck to the total reflectionface 11A by the sticking preventing layer 15 or the high speed ofdriving can be sufficiently kept, it is not always necessary to use thelower substrate 21.

In the optical switching element using only the total reflection lightP₃ with respect to the incident light P₁, in the case where a lightabsorbing layer is formed on a face opposite to the light extractingface of each of the light extracting portions 17 a, 17 b, 17 c, and 17d, the lower substrate 21 having no total reflection face does notalways have to be a glass substrate but may be a silicon (Si) substrate.Obviously, in this case, it is unnecessary to use the transparentelectrode or form an opaque electrode so as to avoid only a lighttransmitting portion.

Referring to FIGS. 23A and 23B to FIGS. 29A and 29B, modifications ofthe foregoing embodiment will be described hereinbelow. The samecomponents as those in the embodiment are designated by the samereference numerals and their description will not be repeated. Since thebasic configuration, action and effects are similar to those in theforegoing embodiment, only different parts will be described in thefollowing.

Each of FIGS. 23A and 23B to FIGS. 25A and 25B shows an opticalswitching element capable using both total reflection light by the uppersubstrate 11 and the transmission light of the light extracting portions17 a, 17 b, 17 c, and 17 d. FIGS. 26A and 26B show an optical switchingelement capable of using only transmission light. FIGS. 27A and 27B showan optical switching element basically using only transmission light butcan use total reflection light as well. Each of FIGS. 28A and 28B andFIGS. 29A and 29B shows a switching element capable of using only thetotal reflection light.

[First Modification]

In the optical switching element shown in FIGS. 23A and 23B, in place ofthe V-shaped grooves 11 a and 11 b used to make the light P₁ incident atan angle the light can be totally reflected by the under face of theupper substrate 11 in FIGS. 21A and 21B, a cylindrical lens 41 having acenter on the under face of the upper substrate 11 is used. In theoptical switching element, the light P₁ can be made incident at an angleso as to be totally reflected by the under face of the upper substrate11. The angle and size of the tapered portion 20 a formed on the lightextracting portions 17 a, 17 b, 17 c, and 17 d have to be set to valuesdifferent from those in FIGS. 21A and 21B.

[Second Modification]

In an optical switching element shown in FIGS. 24A and 24B, in place ofthe V-shaped grooves 11 a and 11 b in FIGS. 21A and 21B, a microprism 42having an isosceles trapezoid in cross section is used. When the lightincident angle is the same as that in the case of FIGS. 21A and 21B andthe inclined face of the trapezoid cross section is perpendicular to thelight incident angle (that is, the inclined angle of each of theV-shaped grooves 11 a and 11 b of FIGS. 21A and 21B and the inclinedangle of the trapezoid cross section are equal to each other), thestructures of the light extracting portions 17 a, 17 b, 17 c, and 17 d,and the other components except for the upper substrate 11 may be thesame as those in FIGS. 21A and 21B.

In the optical switching element shown in FIGS. 25A and 25B, in place ofthe V-shaped grooves 11 a and 11 b of FIGS. 21A and 21B, a microprism 43having an isosceles triangle in cross section is used for each of thelight incident portion and the total reflection light emitting portion.In a manner similar to FIGS. 24A and 24B, when the light incident angleis the same as in FIGS. 21A and 21B and the base angle of the isoscelestriangle cross section is perpendicular to the incident angle of light(that is, when the inclination angle of the V-shaped grooves 11 and 11 bin FIGS. 21A and 21B and the base angle of the isosceles triangle crosssection are equal to each other), the structures of the light extractingportions 17 a, 17 b, 17 c, and 17 d and other components except for theupper substrate 11 may be quite the same as those in FIGS. 21A and 21B.

In the optical switching element shown in FIGS. 26A and 26B, in place ofthe V-shaped groove 11 b on the light emitting side of the uppersubstrate 11 in FIGS. 21A and 21B, a light absorbing layer 44 isprovided. Since the total reflection light P₃ from the bottom face ofthe upper substrate 11 is absorbed by the light absorbing layer 44, theoptical switching element can be effectively used only for thetransmission light P₂ from the light extracting portions 17 a, 17 b, 17c, and 17 d.

In the optical switching element shown in FIGS. 27A and 27B, the angle θformed between the V-shaped groove 11B on the light emitting side of theupper substrate 11 and the top face of the upper substrate 11 is set toan angle so that, different from the V-shaped groove 11 a on theincident side, the total reflection light P₃ travels in the substratealmost in parallel with the top face of the substrate. For example, whenthe incident angle of the incident light P₁ with respect to the uppersubstrate 11 is set to 45 degrees, it is sufficient to set the angle θto be equal to 157.5 degrees. By the setting, the total reflection lightP₃ from the under face of the upper substrate 11 is again totallyreflected by the V-shaped groove 11 b, travels in the upper substrate11, and is led to the outside of the substrate. The light can be alsoused as light absorbed or switched by an end face of the substrate orthe outside of the substrate. In the case where various structures aremanufactured on the upper substrate 11, once light enters thestructures, it becomes noise or attenuates, so that attention has to bepaid.

In the optical switching element shown in FIGS. 28A and 28B, in place ofthe tapered portion 20 a formed on the light extracting portions 17 a,17 b, 17 c, and 17 d in FIGS. 21A and 21B, a light absorbing layer 45 isformed. The optical switching element absorbs the light P₂ passedthrough the light extracting portions 17 a, 17 b, 17 c, and 17 d fromthe upper substrate 11 by the light absorbing layer 45 and makes onlythe total reflection light P₃ valid. Obviously, in the switchingelement, it is unnecessary to provide the tapered portion in each of thelight extracting portions 17 a, 17 b, 17 c, and 17 d.

In the optical switching element shown in FIGS. 29A and 29B, a lightabsorbing layer 46 is formed in a portion on which light P₂ passedthrough the light extracting portions 17 a, 17 b, 17 c, and 17 d on thelower substrate 21 falls. By the operation, an optical switching elementin which only the total reflection light P₃ is valid can be obtained.

The modifications have been described above. Not only the combination ofthe V-shaped groove and the light absorbing layer but also a combinationof a microprism or cylindrical lens and a light absorbing layer can beapplied.

[Image Display]

FIG. 30 shows the configuration of a projection display as an example ofan image display using the switching element 10 or the switching device1. An example of using the total reflection light P₃ from the switchingelement 10 for displaying an image will be described here. Obviously,the transmission light P₂ of the light extracting portions 17 a, 17 b,17 c, and 17 d can be used.

This projection display comprises light sources 31 a, 31 b, and 31 c ofred (R), green (G), and blue (B), respectively, switching element arrays32 a, 32 b, and 32 c provided for the corresponding each light sources,mirrors 33 a, 33 b, and 33 c, a projection lens 34, a galvanometermirror 35 as a uniaxial scanner, and a screen 36. The light sources 31a, 31 b, and 31 c of RGB employs a method of using RGB lasers, a methodof producing RGB light from light emitted from a white light source byusing a dichroic mirror, a color filter, or the like. The three primarycolors may be, not only red, green and blue, but also cyan, magenta, andyellow. In each of the switching element arrays 32 a, 32 b, and 32 c, anecessary plural number of, for example, one thousand of switchingelements 10 are one-dimensionally arranged, thereby constructing a lightvalve (spatial light modulator).

In the projection display, light emitted from the light sources 31 a, 31b, and 31 c of RGB is incident on the optical switching element arrays32 a, 32 b, and 32 c, respectively. The total reflection light P₃ fromthe optical switching elements 10 is condensed by the mirrors 33 a, 33b, and 33 c to the projection lens 34. The light condensed by theprojection lens 34 is scanned by the galvanometer mirror 35 and isprojected as a two-dimensional image onto the screen 36.

As described above, in the projection display, the plurality of opticalswitching elements 10 are arranged one dimensionally and irradiated withlight of RGB, and switched light is scanned by the uniaxial scanner,thereby enabling a two-dimensional image to be displayed.

In the optical switching element 10 having the four thin ribbon-shapedlight extracting portions 17 a, 17 b, 17 c, and 17 d of different widths(areas), which can be independently driven as described in theembodiment, gradation display of 241 levels under digital control inwhich the area gradation display and the gradation display by timedivision are combined is performed in the same pixel. Thus,ultra-high-definition gradation display can be performed with highaccuracy.

Since the response of the optical switching element 10 is sufficientlyhigh, it is also possible to display a color image by using one opticalswitching element one-dimensional array for RGB colors and irradiatingthe optical switching element one-dimensional array with the RGB lightwhile switching the light in a time-division manner.

Although the invention has been described above by the embodiment andmodifications, the invention is not limited to the embodiment andmodifications but can be variously modified. For example, as the opticalswitching device 1, the structure in which the optical switchingelements 10 are one-dimensionally arranged is used in the foregoingembodiment. Instead, an optical switching device 1 in which the opticalswitching elements 10 are arranged two-dimensionally may be used.

In the foregoing embodiment, the example in which the number of lightextracting portions constructing one pixel is four and the lightextracting portions have different widths (areas) at the ratio of1:2:4:8 has been described. The number of light extracting portions isnot limited as long as it is plural. Some or all of the light extractingportions may have the same width. In the case where the plurality oflight extracting portions constructing one pixel have the same width,the number of light extracting portions has to be large to obtain adriving frequency reduction effect similar to that in the embodiment. Onthe contrary, it is sufficient to form a plurality of the lightextracting portions of the same structure in the process ofmanufacturing the light extracting portions, so that the manufacturebecomes much easier.

Although the example of using the optical switching element of theinvention for the display has been described in the embodiment, theoptical switching element of the invention can be also applied to adevice other than the display, for example, an optical printer forforming an image onto a photosensitive drum.

As described above, according to the invention, the optical switchingelement or the optical switching device has: a total reflection memberhaving a total reflection face by which incident light can be totallyreflected; and a plurality of translucent thin light extracting portionsconstructing one pixel, each of which can be switched between a firstposition at which the light extracting portion comes into contact withor is close to the total reflection face of the total reflection memberin a distance in which near field light can be extracted and a secondposition apart from the total reflection face by more than the distancein which the near field light can be extracted. Consequently, the lightextracting portions as movable portions can be formed small and light,so that high response can be achieved. Since the position of each of theplurality of light extracting portions constructing one pixel can beselectively switched, gradation display by area gradation can berealized.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

1. An optical switching element comprising: a total reflection memberhaving a total reflection face by which incident light can be totallyreflected; and a plurality of translucent light extracting portionsconstructing one pixel, each of which can be switched between a firstposition at which the light extracting portion comes into contact withor is close to the total reflection face of the total reflection memberin a distance in which near field light can be extracted and a secondposition apart from the total reflection face by more than the distancein which the near field light can be extracted, wherein areas of facesfor extracting incident light of at least two of the plurality of lightextracting portions are different from each other.
 2. An opticalswitching element according to claim 1, wherein areas of faces forextracting incident light of all of the plurality of light extractingportions are different from each other.
 3. An optical switching elementaccording to claim 2, wherein a ratio of the areas of the faces forextracting the incident light of the plurality of light extractingportions is 2^(n) (where n is an integer of 0 or larger).
 4. An opticalswitching element comprising: a total reflection member having a totalreflection face by which incident light can be totally reflected; aplurality of translucent light extracting portions constructing onepixel, each of which can be switched between a first position at whichthe light extracting portion comes into contact with or is close to thetotal reflection face of the total reflection member in a distance inwhich near field light can be extracted and a second position apart fromthe total reflection face by more than the distance in which the nearfield light can be extracted, and driving means for displacing the lightextracting portion to either the first position or the second positionin accordance with the leading direction of the incident light, whereinthe total reflection member is a translucent substrate having a pair ofparallel faces one of which is a light incident face and the otherserving as either a total reflection face when the light extractingportion is in the second position or a light emitting face when thelight extracting portion is in the first position, and wherein a pair ofV-shaped grooves are provided on the light incident face side of thetranslucent substrate, the incident light is led by one of the V-shapedgrooves to the total reflection face, and reflection light from thetotal reflection face is led to the outside by the other V-shapedgroove.
 5. An optical switching element comprising: a total reflectionmember having a total reflection face by which incident light can betotally reflected; and a plurality of translucent light extractingportions constructing one pixel, each of which can be switched between afirst position at which the light extracting portion comes into contactwith or is close to the total reflection face of the total reflectionmember in a distance in which near field light can be extracted and asecond position apart from the total reflection face by more than thedistance in which the near field light can be extracted, wherein on aface on the side opposite to the total reflection member side of thelight extracting portion, a total reflection preventing portion forpreventing total reflection by the light extracting portion of incidentlight passed through the total reflection member when the lightextracting portion is in the first position is provided, and wherein thetotal reflection preventing portion is a translucent tapered portionhaving an angle at which total reflection does not occur, for leadingincident light in a direction opposite to the total reflection memberside.